The present invention relates generally to ball valves, and more particularly, to a ball valve having a one-piece machined seat member such that the incidence of leakage is reduced and the ball valve is highly reliable.
Typically, in a ball valve, a seat member is positioned within a valve chamber to seal and selectively isolate two or more ports leading to the valve chamber. The seat member substantially surrounds a metal or plastic ball member, and an operating stem extends from the ball member. The valve is operated by rotating the stem to selectively align two or more of the ports with corresponding passages in the ball member.
It is known to form the seat member around the ball member by positioning the ball member between upper and lower seat member pieces and then welding, fusing, or otherwise joining the upper and lower seat member pieces to each other. However, a recurring problem with a ball valve having such a two-piece seat member is that leakage occurs at the juncture of the pieces.
It also is known to employ injection molding techniques to form a one-piece seat member around the ball member. However, the injection molding results in a joining line on the external surface of the seat member, and the joining line is susceptible to damage from pressure, temperature, use, and chemicals sealed by the valve, among other things. When damaged, the joining line breaks down and allows leakage in the ball valve.
A need exists, then, for a ball valve with a seat member that reduces the likelihood of leakage at the joining line. More particularly, a need exists for a ball valve with a one-piece seat member that does not have a joining line.